Capacitive discharge ignition system

ABSTRACT

An ignition system for internal combustion engines utilizing a capacitive discharge to supply energy to the spark plugs. Charging and discharging of the capacitor is controlled by a circuit utilizing a silicon controlled rectifier which operates in response to the contact breaker for turning on and in response to positive back-biasing for turning off. The system automatically adjusts spark characteristics to accommodate changes in engine environment and running conditions.

United States Patent 1191 Jacobs Feb. 13,1973

[ CAPACITIVE DISCHARGE IGNITION SYSTEM [76] Inventor: Christopher A.Jacobs, 1328- 2 West 24th Street, Los Angeles, Calif. 90007 [22] Filed:Oct. 15, 1969 [21] Appl. No.: 866,626

[52] US. Cl ..l23/l48 E, 123/148 R [51] Int. Cl ..F02p 1/00 [58] Fieldof Search ..l23/l48 E, 179 P, 179 G;

[56] References Cited UNITED STATES PATENTS 3,496,921 2 1970 Boyer..123/148 E 3,543,109 11/1970 Minks..... ....123/148 E 3,560,833 2/1971Oishi ....123/148 E 3,575,153 4 1971 Hardin... ....123/148 E 3,581,726 61971 Plume..... ..123 148 E 2,847,489 8/1958 Short 123/148 3,049,6428/1962 Quinn ..l23/l48 3,251,351 5/1966 Bowel-Sm. ....123/148 3,331,9867 1967 Hardin ....123/148 3,502,955 3 1970 Minks ....123/148 3,134,0485/1964 Wolfframm et a1. ....123 148 3,312,060 4/1967 Strum 123/1483,357,415 12/1967 Huntzinger .l23/148 3,487,822 10/1970 Huftonetal...123/l48 FOREIGN PATENTS OR APPLICATIONS 582,384 9/1959 Canada..l23/I48 OTHER PUBLICATIONS Electronics Magazine, 10/5/64, A NewIgnition System for Cars.

Radio Electronics Electronic Ignition for Your Car 9/61.

Primary ExaminerLaurence M. Goodridge Assistant Examiner-Ronald B. CoxAttorney-Christie, Parker & Hale [5 7] ABSTRACT An ignition system forinternal combustion engines utilizing a capacitive discharge to supplyenergy to the spark plugs. Charging and discharging of the capacitor iscontrolled by a circuit utilizing a silicon controlled rectifier whichoperates in response to the contact breaker for turning on and inresponse to positive back-biasing for turning off. The systemautomatically adjusts spark characteristics to accommodate changes inengine environment and running conditions.

7 Claims, 2 Drawing Figures PATENIEUFEBU I915 v 3,716,037

I N VENTOR.

CAPACITIVE DISCHARGE IGNITION SYSTEM DESCRIPTION OF THE PRIOR ART Thepresent invention relates to ignition systems for internal combustionengines and in particular to an ignition system utilizing a capacitivedischarge to supply energy to the spark plugs of the engine.

Among the various ignition systems which have been tested and/orproduced as equipment for automobiles, particularly those manufacturedin theUnited States, the most common system is that generally known asthe Kettering ignition system. In the Kettering system, the collapse ofa magnetic field in the primary winding of an ignition coil induces ahigh voltagein a secondary winding of the coil which is transmitted viaa distributing arrangement in sequence to a series of spark plugs toignite a fuel mixture in the engine cylinders. The collapse of energy inthe primary of the ignition coil is controlled by a contact breaker andcam arrangement with current flow being interrupted and a burst ofenergy supplied by the ignition coil each time the cam causes thecontact breaker to open. Energy is supplied to the primary of theignition coil from a conventional power source such as a 6 or 12 voltwet cell battery. In more recent versions of the Kettering system,electronic elements are utilized to perform certain switching functionsas well as in power supplies which, in some instances, are beingutilized in such ignition systems to improve operating characteristics.Such recent versions age pulse at the secondary side of an ignitioncoil, the

system utilizes a capacitor as the primary energy source. Energy issupplied thereto for storage 'until released as a high energy pulse tothe spark plugs. Typically, such ignition systems include a vibrator orinverter utilizing vacuum tubes or semiconductor devices in the circuitbetween the battery and the energy storage capacitor. Under control ofthe contact breaker points and an electronic switching device such as asilicon controlled rectifier, the capacitor previously charged by theinverter is then discharged into the primary side of an ignition coilcausing a high voltage pulse to be produced on the secondary side of thecoil and a high voltage spark at the plugs.

Heretofore, capacitive discharge ignition systems have had problemsassociated with them due to the method of discharging the capacitor intothe coil. Such problems are products of the actual design of the systemand are not due to any inherent problem in this type of ignition system.There is no theoretical reason why an ignition system utilizing thedischarge of a capacitor cannot perform at a level of reliability whichis comparable to the best performance of the more conventional systemsthereby making available the superior spark I quality of capacitivedischarge ignition systems and their ability to produce firing of thespark plugs despite changes in plug condition whether due to age,wetting or fouling in a unit of satisfactory reliability.

SUMMARY OF THE PRESENT INVENTION The present invention provides anignition system for internal combustion engines comprising a highvoltage power supply connected to capacitive means for storing electricpower. Means for coupling the capacitive means to an ignition coil areprovided and control circuit means including an electronic switch iscoupled to the coupling means and the capacitive means for closing theswitch to discharge the capacitive means. Finally, means for positivelyopening the electronic switch is provided for causing the capacitivemeans to be recharged.

In prior art capacitive discharge ignition systems, significant problemshave been encountered in turning off an electronic switch utilized torelease energy from the energy storage capacitor, in protecting theswitch and in obtaining reliable recharging of the capacitor. In the twogeneral approaches heretofore adopted, the first has utilized theprinciple of interrupting power from the inverter and the second hasoperated on the principle of back-biasing the switch (which is normallya silicon controlled rectifier) by means of currents which areproducedin the ignition coil. Each approach is subject to difficulties. In theformer, it is virtually impossible to accurately know when to turn theinverter on and off and be able to do it rapidly enough. This is due tothe changing inductive properties of the coil and changing enginespeeds. If the inverter is turned on too soon after the capacitordischarge, the SCR becomes locked on and the ignition system ceases tooperate. If the turnon is delayed too long, there is insufficient timeto recharge the capacitor for satisfactory firing of the next sparkplug. The latter approach utilizes the inductance of the ignition coilwhich is subject to unpredictable change and, therefore, cannot berelied on to turn off the switch. In addition, a significant change inthe condition of the coil, such as a short across a pair of terminals orwetting of the terminals can also produce a current surge which coulddamage or destroy the electronic switch.

The present invention avoids the problems previously characteristic ofcapacitive discharge ignition systems and provides a system whichutilizes the good qualities of a silicon controlled rectifier as theelectronic switch controlling the discharge of energy from the capacitorwhile providing additional supporting circuitry' to overcome theaforementioned problems. Shut-off of the silicon controlled rectifier isachieved by a back-bias technique, but instead of relying only upontransient current within the ignition coil after a discharge of thecapacitor to accomplish this result, the circuit of the presentinvention provides additional means for insuring that the SCR'isback-biased a sufficient length of time to produce shut-off regardlessof changes in the characteristics or parameters of the ignition system,particularly changes in the ignition coil. The ,circuit, moreover,embodies within it the capability of channeling the residual energywhich is left in the ignition coil after production of the spark tobegin the recharging process of the energy storage capacitor. Positiveshut-off of the SCR is further assured by the provision of diodecircuitry connected to the silicon controlled rectifier in a specificmanner. This diode circuitry also acts to reduce or eliminate anyresidual magnetism in the core of the ignition coil. The system embodieswithin itself positive protection for the electronic switch against thepossibility of damage due to sudden current or voltage surges,occurrences which are a significant cause of SCR failure. Finally,positive protection against the possibility of the SCR firing at thewrong time is provided by means of a control circuit coupled between thebreaker points of the ignition system and the semiconductor switch.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF A SPECIFIC EMBODIMENT Afunction and circuit diagram of an ignition system is shown in FIG. 1.The positive pole of a battery 11 is connected by an input connection 12through an ignition switch 13 to a capacitive discharge ignition systemaccording to the present invention. A first output 9 of capacitivedischarge system 10 is connected to the primary winding of an ignitioncoil 42 and a second output 44 to the ignition or contact breaker points15. The secondary winding of coil 42 is connected to a rotor 21 of aconventional distributor which, in turn, has a plurality of contacts 25,each connected to a spark plug 23. As will be described in more detailin conjunction with FIG. 2, the ignition system of FIG. 1 utilizes thedischarge of energy from a storage capacitor within system 10 throughcoil 42 and rotor 21 to the spark plugs 23. Cam 17 of the contactbreaker rotates and opens the breaker points causing the storagecapacitor to discharge and energy to be supplied to the plugs. System 10also includes circuitry whereby the discharge path from the energystorage capacitor is interrupted to permit capacitor recharging for thenext succeeding spark interval.

A capacitive discharge ignition system 10 according to the presentinvention is shown in schematic form in FIG. 2. Power from a source suchas a I2-volt battery is supplied by an input connection 12 and a fourpin plug 14 on the unit. An inductor 16 is connected between the inputconnection I2 and an inverter or oscillator 29. Inverter 29 includes apair of transformers 20 and 24 having center tapped primary andsecondary windings, respectively, with the center taps being connectedto one another by a resistor 22. Inductor I6 is connected to the side ofresistor 22 adjacent transformer 20. A diode 26 connects the side ofresistor 22 opposite transformer 20 to ground; Inverter 29 furtherincludes a pair of transistors 31, 33 having their base electrodesconnected to opposite ends of the secondary winding of transformer 24,their collector electrodes to opposite ends of the primary winding oftransformer 20 and their emitter electrodes to the opposite ends of theprimary winding of transformer 24.

The output of inverter 29 is taken from the secondary winding oftransformer 20 and connected to the input terminals ofa full waverectifier-28. The output of rectifier 28 is in turn connected by meansof an inductor 30 and a resistor 32 to an energy storage capacitor 34.The side of resistor 32 adjacent capacitor 34 is also connected by meansof a temperature sensitive switch 36 to a second energy storagecapacitor 38 and through a parallel diode 78-resistor combination to athird energy storage capacitor 76. Capacitors 34, 38 and 76 are in turnconnected in common to one side of an inductor 35, the opposite of whichis connected by a circuit connection 37 through plug 14 to the primarywinding 43 of ignition coil 42. An inductor 74 is connected between theside of inductor 35 opposite the common connection thereof to the threeenergy storage capacitors 34, 38 and 76 and a circuit ground or commonpoint. The portion of the circuit just described traces the path ofenergy supplied from the battery through the energy storage capacitor ofthe system of the present invention preparatory to discharge and thesupplying of energy through the ignition coil to the spark plugs toprovide combustion of the fuel mixture in the engine cylinders.

The control portion 39 of the circuitry of the present inventioncomprises a silicon controlled rectifier 40 and a pulse shaping circuit50 which is connected between a gate electrode 41 of SCR 40 and lead 44extending through plug 14 to the breaker points 15. Control circuit 39is also connected on one side by means ofa circuit connection from theanode 56 of the SCR to the side of resistor 32 common to capacitor 34 atone side and on its other side to a resistor 18 and the power inputconnection 12. When the breaker points are closed, current flowing fromthe battery through plug 14 and resistor 18 is shorted to ground throughthe points. When the points open, current from the battery is directedthrough the pulse shaping circuitry 50 of control circuit 39 and thenceto the gate electrode 41 of the silicon controlled rectifier 41 (SCR) tocause the SCR to be turned on. A discharge path for energy in storagecapacitor 34 is thereby provided, the path including the primary 43 ofignition coil 42, inductor 35, capacitor 34 and SCR 40. Upon dischargeand energy flow, a high voltage pulse is induced in the secondarywinding 45 and an ignition spark produced at one of the engine sparkplugs.

The circuit also incorporates within itself a mode of operation forturning the SCR off after a surge of energy from capacitor 34 has beensupplied responsive to opening of the breaker points. The method ofturning the SCR off according to the present invention is to back-biasthe SCR, i.e, reverse the voltage so that the current attempts to go upthrough the SCR from ground toward capacitor 34. Since SCR 40, capacitor34 and the primary winding 43 of coil 42 which acts as an inductor arein series, there is a natural tendency for the desired back-biasing tooccur. After the initial spark energizing surge of power from storagecapacitor 34, the side of the capacitor adjacent coil 35 assumes apositive charge and has a tendency to drive current down through thecoil and up through the SCR (reverse direction), the net effect of thiscircuit action being to shut the SCR off. i

To assure positive shut-off, it is necessary that the SCR be back-biaseda predetermined minimum length of time (the specified SCR turnoff time)after every discharge of the capacitor. To obtain such .assurance, acoil 35 of a predetermined inductance is inserted in series between theprimary 43 of coil 42 and the energy storage capacitor 34. Due to theadditional inductance contributed by coil 35, the series SCR40-capacitor 34- primary winding 43 circuit now maintains itsback-biasing polarity a sufficient length of time to insure that the SCRwill turn off even in the extreme case where the inductance of winding43 goes to zero. Thus, despite any problem which may lower theinductance of the primary of coil 42, for example, water splashed on thecoil, a short-circuit causing the hot side of the coil to be grounded tothe case, grease and road grime build-up or carbon tracking from thehigh voltage terminal, in short, any problem tending to reduce theinductance of the primary of the ignition coil will not affect thebackbiased turnoff capability of the circuit.

Inductor 74 is connected to the junction of inductor 35 and primarywinding 43 for the purpose of further ensuring that the SCR is turnedoff. Under certain circumstances (particularly at high engine. speeds),the primary of the ignition coil acts as if it were a very highinductance and severely retards the ability of capacitor 34 todischarge. Provision of inductor 74 provides an inductance in parallelwith primary winding 43 and this limits the maximum inductance of thecombination (even where the inductance of winding 43 appears to beinfinite) to that of inductor 74. By proper choice of the inductancevalue of coil 74, discharge of the energy storage capacitor is stillaccomplished thereby assuring sufficient back-biasing current for SCRturnoff during the immediately subsequent back-biasing portion of systemoperation.

Inductor 35 provides an additional and important contribution to theignition system by acting as a device for limiting current to the SCR.By providing an inductor of a predetermined magnitude, e.g., 270micro-henries, the current through the SCR is maintained at a maximum of60 amps or less, even where the inductance of winding 43 has gone tozero. Again, even under the most adverse circumstances of circuitoperation, the current to the SCR is limited to a value which can easilybe absorbed by the SCR. The net result of the provision of inductors 74and 35 is that no change in ignition coil properties can cause the SCRto fail to turn off or to cause it to be damaged due to current surges.

The circuit of the present invention also incorporates the capability ofutilizing the transient energy remaining in the circuit subsequent toeach storage capacitor discharge to recharge capacitor 34 to a partialvalue of .its total charge without the necessity of drawing energy fromthe oscillator 28 (inverter). Harnessing the residual energy in acircuit to partially recharge the energy storage capacitor is beneficialin reducing wear on the inverter circuit and battery current drain bydrawing less current therefrom as well as in checking spark plug erosionwere the transient energy not channeled back to capacitor 34.

The foregoing is accomplished by providing a pair of diodes 52 and 54 inseries connected between a ground connection and the anode 56 of SCR 40.Upon turning on the SCR, a discharge path to ground is provided andcurrent flows up through the primary of coil 42 and inductor 35 untilthe potential on the side of capacitor 34 adjacent coil 35 is reduced tozero. At this instant a significant amount of energy is stored in theprimary of coil 42 and in inductor 35 which, unless dissipated in someconstructive manner, produces undesirable oscillation in the ignitionsystem. Current continues to flow to winding 43 and inductor 35 andcapacitor 34 charges in the opposite direction. At its maximum oppositecharge (approximately 350 volts relative to inductor 35) the current ininductor 35 and winding 42 is zero. The reverse charge on capacitor 34then begins to drive current in the opposite direction through coil 35and winding 42. By providing diodes 52 and 54, a current path isprovided such that when the current reverses and begins to flow in theopposite direction through the inductor 35 and the primary of coil 42,storage capacitor 34 is thereby recharged to approximately 75 percent ofits fully charged value without drawing power from the inverter. Thecurrent path through diodes 52, 54 also provides a means whereby anytendency of the coil to build up residual magnetism is reduced oreliminated as well as tending to protect against ignition coilinsulation breakdown. (At the end of each discharge cycle the currentthrough the coil has traced one nearly perfect sine wave pattern).

' Diodes 52 and 54 perform a third function in assuring that the SCR 40is shut off. Because there is approximately a 1 volt drop across each ofthe diodes and the cathode 58 of SCR 40 is permanently connected toground, current up through diode 54 from ground (during the reversecurrent portion of circuit operation) produces a minus one volt (-1.Ov.) potential with respect to ground on the gate 41 of the SCR anddiode 52 produces a second 1 volt drop, simultaneously placing the anodeat a potential of minus 2 volts (-2.0v.) with respect to ground and at apotential of minus 1 volt (-1 .Ov.) with respect to the gate electrode41. The SCR is thus fully back-biased and is thereby shut off in theminimum time possible.

A further advantage of the circuit of the present invention is itsability to channel and dissipate high voltage energy spikes-which wouldotherwise have the tendency to damage or destroy the SCR. Under normaloperating conditions, when energy is supplied to the spark plug and anarc-over occurs, the energy supplied by the storage capacitor isdissipated in the spark plug gap and only a relatively small ainount ofenergy is left in the secondary 45 of the ignition coil. However, whenthe circuit fails to produce a spark at the plug (no arcover), e.g.,when spark plug condition has seriously deteriorated, the energywhichwould ordinarily have been transmitted to the spark plug gap isstored as an extremely high voltage by the capacitive action of thespark plug wires and the ignition coil secondary. If not dissipated,this energy is reflected back to the ignition coil primary 43, capacitor34 and SCR 40 as a high voltage spike. If a sufficient number of suchhigh voltage spikes were allowed to be transmitted to the SCR, seriousdeterioration of the SCR result to the point where the SCR ultimatelystops functioning.

Such an occurrence is prevented in the present circuit by inductor 35which reflects approximately percent of any pulse transmitted fromwinding 43 back toward this winding with the result that this 80 percentof the pulse exhausts itself by bouncing back and forth between inductor35 and coil 43. This is the third function of inductor 35. The remaining20 percent of the energy is transmitted through inductor 35 andcapacitor 34 and toward SCR 40. By providing a very low impedance escapepath through diode 60 to filter capacitor 62 in the inverter, thistransmitted energy is absorbed by capacitor 62 and never reaches theSCR.

Accidental firing of SCR 40 which could cause a premature enginedamaging spark is prevented by the provision of several circuitcomponents in a specific arrangement. In the first instance, a filtercomprised of inductor 16 and capacitor 64 filter out any voltage spikesgenerated by inverter and prevent such spikes from being transmitted tothe SCR. The same filtering action exerted by inductor 16 and capacitor64 also prevents any noise in the form of voltage spikes from the powersource from being transmitted to the inverter, an important precautionin preventing such voltage spikes from passing through the invertertothe anode of the SCR.

A second precaution against premature SCR firing resides in the designof the pulse shaping circuit 50. As indicated earlier, the signal istransmitted to the gate electrode 41 of SCR 40 at the instant the pointsor breaker contacts open. When the points open, current v flows throughresistor 18 and through the parallel combination of resistor 46 anddiode 48 and begins to charge capacitors 66 and 68. The charging timeconstant of capacitors 66 and 68 is chosen such that it allows enoughcurrent to pass through capacitor 68 to fire the SCR even at very lowtemperatures (35 F.) but nevertheless will not pass voltage spikes overcapacitor 66 and through capacitor 68 to the gate of the SCR.

Circuit 50 is also provided with a second stage comprising resistor 72and capacitor 70. Assuming for the moment the possibility that a voltagespike does pass capacitor 66 and resistor 72, capacitor 70, which isconnected in parallel circuit relationship with diode 54, acts to shortcircuit such spikes arriving at that point in the circuit to ground.

In addition to blocking all voltage spikes above a predeterminedvoltage, the parallel combination of resistor 46 and diode 48 alsoprevents point bounce from firing the SCR. Since point bounce occursimmediately after the points close and a signal has been transmittedthrough circuit 50 to the SCR, capacitors 66 and 68 are still in acharged condition and, due to the r nagnitude of resistance 46, have nothad a chance to discharge. Therefore, voltage spikes generated due topoint bounce will not be transmitted to the SCR since it is the processof charging capacitor 68 which causes the SCR to fire. The condition ofcapacitor 68 already being charged thus prevents transmission of thespike to the SCR. Other random voltage spikes introduced into thecircuit, e.g., from the twelve volt source, are also not transmitted tothe SCR because such spikes are diverted to'pass through resistor 18 andthrough the closed set of breaker points to ground. By choosing resistor18 of a sufficiently low value, electromagnetic pickup is not a problemand the resistor further determines the amount of current through theclosed points such that sufficient heat is generated to keep the pointsclean but is limited to a value which will not produce significant wear.4

An important characteristic of the ignition system of the presentinvention is its ability to produce a variable power pulse to the sparkplugs of the engine to suit varying engine conditions. Among otherconditions encountered in a normal operation is a cold engine uponstarting, a tendency of the spark plugs to foul when running the engineat low or idling speeds and wear and deterioration of the various ofcomponents of the ignition system including the ignition coil and sparkplugs. With respect to the first condition, it takes considerably moreenergy to start a cold engine than to run it, once warm, and, therefore,a substantially higher voltage from the energy storage capacitor duringthis interval is desirable. The starting problem is further compoundedby the fact that the battery voltage is normally relatively low at thespecific time when it is required that the energy storage capacitorvoltage be high. As concerns the second condition it is also desirableto provide more energy to the spark plugs at low speeds since suchincreased energy has a tendency to burn fouling material which may begenerated. In addition, if such fouling material does become deposited,there is still sufficient spark energy to fire the fuel mixture in thecylinder despite the energy drain caused by the presence of thismaterial. As the following discussion will disclose, specific portionsof the ignition system of the present invention have been designed tofulfill these desired requirements.

By providing a specific type of core material for transformers 20 and 24of inverter 29, both of these transformers are provided with saturationeffects that are voltage and current dependent. This feature is utilizedto provide an inverter having a voltage characteristic which variesaccording to the varying requirements of the engine with which it isbeing used to vary the electric power supplied to the storage capacitor.Thus, a higher voltage on starting (engine cranking speeds) is provided,with a somewhat reduced voltage when the engine is idling or runningslowly (low and intermediate engine speeds) and a still further reducedvoltage is provided when engine revolutions have risen to a higher speed(normal engine running speeds) at which plug fouling is normally not aproblem. In a typical case, the output voltage from the inverter forengine RPMs from 0 to 250 (starting) with an input voltage from thebattery of from 7.5 to 16 volts is approximately 600 volts. When theengine RPMs are from 400 to 750, that is, idling and very low speed, theoutput voltage of the inverter is inversely proportional to engine speedin the range of 600 volts descending down to approximately 425 volts.When the engine RPMs increase to a value above 750, the inverter outputvoltage further drops to approximately 425 volts and remains at thatvalue over the entire range of engine running speeds, thereby serving tomaintain spark energy constant over this entire range. In contrast, inconventional Kettering ignition systems, spark energy decreases asengine RPM's increase, a serious disadvantage of such systems.

As a further means of increasing spark energy for example, in thesituation of starting a cold engine, the circuit of the presentinvention increases spark energy and spark duration by increasing thevalue of the energy storage capacitor when the engine is cold. This isaccomplished by providing a temperature sensitive switch 36 which isphysically located in position adjacent to resistor 32. Since current inthis resistor is proportional to engine RPM s, resistor 32 warms up atthe rate which closely approximates engine speed. Since the engine warmsup at a rate roughly proportional to its speed, the increase intemperature of resistor 32 closely approximates the increase in enginetemperature. When the temperature is below a critical value, switch 36is closed and capacitor 38 is connected into the circuit increasing theavailable capacitance of the energy storage capacitor. After resistor 32has warmed, and likewise the engine has warmed to the propertemperature, switch 36 opens and the value of the discharge capacitanceis reduced by removing capacitor 38 from the circuit. Increasing thevalue of capacitance not-only increases the amount of energy availablefor delivery to the spark plugs but also lengthens the duration of theignition spark when the engine is cold due to the increased timeconstant of a circuit having an enlarged capacity.

To provide an additional increase in spark energy and duration at lowengine speeds (above the increase supplied by increased inverter outputvoltage at these speeds), a series-parallel circuit comprising acapacitor 76 in series with a parallel combination of a diode 78 and aresistor 80 is connected between the junction of resistor 32 andcapacitor 34 on one side and between the junction of capacitors 34 and38-on the opposite side thereby connecting capacitor 76 in parallelcircuit relationship with capacitors 34, 38. The purpose of this circuitcombination is to produce an additional measure of capacitance by meansof capacitor 76 at low engine speeds (regardless of engine temperature)with the contribution of this portion of the circuit diminishing toessentially zero as engine RPMs reach and exceed 1,000. The operation ofthis portion of the circuit is as follows: At low engine speeds, as theSCR fires, capacitors 34 and 76 (and capacitor 38 when it is connectedin the circuit) discharge providing an increase in energy to the plugs,the discharge of capacitor 76 being obtained through diode 78. Byselective choice of the value of resistor 80, a time constant of this RC80,76 combination can be obtained such that at low engine speeds asignificant charge can be built upon capacitor 76 but at higher enginespeeds, discharge of capacitor 34 occurs so frequentlyas to preventsignificant charge from being accumulated on capacitor 76.

Inductor of the circuit of the present invention enhances the ability ofthe circuit to generate a spark despite the fact that the spark plugsmay be fouled or wetted. The circuit action is accomplished because theSCR stays on for a longer periodof time due to the fact that theeffective inductance and resistance of the coil is increased beforearc-over of the plug occurs and areover in a foul or wetted plug alwaystakes longer than in a clean plug. By virtue of the SCR staying onlonger, a voltage exists across inductor 30 for a longer period of timeand thus a significant amount of energy is stored therein which, whenthe SCR is shut off, is transmitted through the plug gap, tending toflash or burn up the contaminating materials. The remaining portion ofthe energy in inductor-30 is transmitted to capacitor 34 to charge it ata rapid rate making it ready to provide a full measure of energy uponits next discharge despite being heavily drained on the previousdischarge by the contaminated plug.

There is thus provided an ignition system in which the SCR is protectedagainst damage from any eventuality, e.g., voltage or current surges andfurther a system is provided which adapts to changing engine conditionsproviding more or less energy as needed assuring maximum ignitioncapabilities and minimum wear on all system parts as well as minimumplug erosion. Whereas an ignition system designed to deliver maximumenergy to the spark plugs at all times would perform satisfactorily interms of its ignition capabilities, the same would not be true of itseffect on the life and erosion rate of the spark plugs. By incorporatingthe features outlined in the preceding to automatically adjust andcontrol the amount of energy delivered to the plugs during the variousconditions to be encountered by the engine, the system of the presentinvention provides optimum amounts of energy for each such condition.The life of the plugs is thereby extended to an interval which isseveral times greater than the spark plug lifetime in conventionalignition systems or in any system which does not vary spark duration andintensity to suit engine needs. What is claimed is: 1. An ignitionsystem for internal combustion engines comprising:

a high voltage power supply; a capacitive means for storing electricenergy coupled to the power supply; means for coupling the capacitivemeans to an ignition coil; control circuit means including an electronicswitch coupled to the coupling means and the capacitive means forclosing the switch to discharge said capacitive means; and first circuitmeans including an inductor coupled in series with the capacitive meansand the ignition coil, said inductor having an inductance value of amagnitude sufficient to limit the current flowing through the electronicswitch during discharge of the capacitor means independent of theeffective inductance of the ignition coil and sufficient to back biasthe switch after discharge of the capacitor means a sufficient length oftime independent of the effective inductance of the ignition coil tothereby permit the capacitive means to be recharged. 2. An ignitionsystem according to claim 1 wherein the electronic switch is a siliconcontrolled rectifier.

3. An ignition system according to claim 2 wherein the siliconcontrolled rectifier has an anode, a cathode and a gate electrode,including first means for biasing the gate negatively with respect tothe cathode and second means for simultaneously biasing the anodenegatively with respect to gate and cathode during the back biasinginterval.

12 an inductor connected in parallel with a primary winding of theignition coil for assuring discharge of the capacitive means andsufficient back biasing current for the silicon controlled rectifier.

* i l l

1. An ignition system for internal combustion engines comprising: a highvoltage power supply; a capacitive means for storing electric energycoupled to the power supply; means for coupling the capacitive means toan ignition coil; control circuit means including an electronic switchcoupled to the coupling means and the capacitive means for closing theswitch to discharge said capacitive means; and first circuit meansincluding an inductor coupled in series with the capacitive means andthe ignition coil, said inductor having an inductance value of amagnitude sufficient to limit the current flowing through the electronicswitch during discharge of the capacitor means independent of theeffective inductance of the ignition coil and sufficient to back biasthe switch after discharge of the capacitor means a sufficient length oftime independent of the effective inductance of the ignition coil tothereby permit the capacitive means to be recharged.
 1. An ignitionsystem for internal combustion engines comprising: a high voltage powersupply; a capacitive means for storing electric energy coupled to thepower supply; means for coupling the capacitive means to an ignitioncoil; control circuit means including an electronic switch coupled tothe coupling means and the capacitive means for closing the switch todischarge said capacitive means; and first circuit means including aninductor coupled in series with the capacitive means and the ignitioncoil, said inductor having an inductance value of a magnitude sufficientto limit the current flowing through the electronic switch duringdischarge of the capacitor means independent of the effective inductanceof the ignition coil and sufficient to back bias the switch afterdischarge of the capacitor means a sufficient length of time independentof the effective inductance of the ignition coil to thereby permit thecapacitive means to be recharged.
 2. An ignition system according toclaim 1 wherein the electronic switch is a silicon controlled rectifier.3. An ignition system according to claim 2 wherein the siliconcontrolled rectifier has an anode, a cathode and a gate electrode,including first means for biasing the gate negatively with respect tothe cathode and second means for simultaneously biasing the anodenegatively with respect to gate and cathode during the back biasinginterval.
 4. An ignition system according to claim 3 wherein said firstand second biasing means are a pair of diodes, said pair of diodes beingconnected in series circuit relationship between a source of referencevoltage and the anode of the silicon controlled rectifier, the gate ofthe silicon controlled rectifier being connected to the junction betweenthe series connected diodes.
 5. An ignition system according to claim 4including second circuit means coupled to the first circuit means andthe silicon controlled rectifier for preventing high voltage spikesignals present in the ignition system from reaching the siliconcontrolled rectifier.
 6. An ignition system according to claim 5 whereinthe second circuit means includes a unidirectional current carryingdevice connected so as to conduct current in a direction away from thesilicon controlled rectifier.